SCIENCE WATCH

SCIENCE WATCH; Cancer and Seasons

Published: May 26, 1992

A new study of mice has found a possible link between the development of cancer and the changing of seasons.

The study, conducted by two psychologists at Johns Hopkins University, Joan Blom and Dr. Randy Nelson, showed some animals may be able to resist cancer by bolstering their immune system during the short days of winter.

To test their hypothesis, Ms. Blom and Dr. Nelson separated 50 female deer mice into two groups and exposed them to lighting periods simulating summer and winter. This, said Dr. Nelson, is because light, rather than temperature, is a more accurate indicator of seasons.

After eight weeks, the mice were injected with 9,10-dimethybenzanthracene or DMBA, a carcinogen. Within a month 85 percent of the mice exposed to long periods of light developed skin cancers and mammary tumors, but none of the mice exposed to short periods did. Blood tests also showed higher white blood cell counts in mice in the latter group, suggesting that their immune systems were stronger.

This may be attributed to melatonin, a hormone that has been shown to stop the growth of some cancer cells, Dr. Nelson said. Studies have shown melatonin is released in more sustained bursts at night.

Dr. Nelson said experiments were under way to determine the effects of the hormone. If a correlation is found between melatonin and exposure to different periods of light it may help explain the seasonal variations in tumor diagnoses and their sizes. He said he hoped their study would lead to therapies that could improve cancer treatments by careful manipulation of the environment.